Damped electrohydraulic servo valve



7 Claims. (Cl. rev-s2 This invention relates to electrohydraulic servo valves of the type in which a light, movable armature of a sensitive electromagnetic motor or relay varies the position of a flow-impeding eiement with respect to a new nozzle, to thereby produce pressure changes for hydraulic actuation of a valve controlling a hydraulic motor.

The function of a servo valve of this type is to control a relatively large amount of hydraulic power with a very weak electric signal that may change rapidly. it is found that when such servo valves are designed for extreme sensitivity and rapid response, they tend to become unstable and oscillate or sing spontaneously.

An object of the invention is to improve the stability of electrohydraulic servo valves.

A feature of the invention is an electrohydraulic servo valve of the type having a magnetically actuated armature controlling a flow nozzle, in which the armature is movably supported by leaf spring elements of such area that rapid movement thereof is damped by the resistance of the ambient fluid.

Other more specific objects and features of the invention will appear from the description to follow with reference to the drawing, in which:

Fig. l is a schematic diagram of a system incorporating a valve in accordance with the invention.

Fig. 2 is a view taken in the plane 11-11 of Pig. 1.

Fig. 3 is a view taken in the plane Il1-lll of Fig. 1.

The present invention is shown applied to an electrohydraulic servo valve of the type disclosed in my application Serial No. 437,778, filed June 18, 1954, to which reference is made for details not specifically relating to the present invention.

The system shown in Fig. 1 consists of an electrohydraulic servo valve incorporating the invention, for selectively controlling flow of pressure fluid from a pump 11 to either end of a load cylinder 12 and returning fluid from the other end of the load cylinder to a reservoir 13 which supplies the pump.

The lower portion 14 of the valve 1% comprises a conventional spool or shuttle-type four-way valve consisting of a valve cylinder 15 containing a pressure-actuated valve piston 16 movable from a central neutral position into either of two end positions. In the left end position of the piston 16, an annular groove 16a therein connects an annular pressure port 15a in the cylinder to one annular motor port 15b, and an annular groove 16b in the piston connects another annular motor port 150 to a return port 15d, so that the piston of the load cylinder 12 is driven to the left. In the right end position of the valve piston 16, the groove 16!; thereof connects the pressure port 15a to the motor port 150, and the piston groove 16a connects the motor port 1512 to a return port 152, so that the piston of the load cylinder 12 is driven to the right. in the neutral position of the valve piston 16, as shown in Fig. 1, the grooves 160 and 1:65 of the piston are isolated from both the pressure port 15a and the motor ports 15d atnd 15c, so that the piston of the load cylinder 12 is locked in position.

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2327,05? Patented Mar. 18, 1958 The valve piston 16 is normally held in neutral position by helical compression springs 18 and 19 slightly compressed between the opposite ends of the piston and the adjacent ends of the cylinder. The piston is movable in either direction out of neutral position against the restraining force of the springs 13 and 19 by admitting fluid of different pressures to the opposite ends of the cylinder 15 through passages 20 and 21, the relative pressures in which are controlled by an electromagnetic valve mechanism in the upper portion 22 of the valve 19.

This upper portion 22 contains an electromagnetic motor or relay having a stationary field structure 23 and a movable armature element 24, and a driving coil 25 surrounding the armature element 24, the latter being of soft iron or similar material such that it is readily magnetized and demagnetized in response to changes in the current in the winding 25. The field structure 23 comprises a pair of iron pole pieces 23a and 23b of general U-shape so associated with a pair of permanent magnets 53 and 54 that the upper pole piece 23a has a north pole at each end adjacent the armature, as indicated by the reference letters N, N, and the pole piece 2317 has a south pole at each end adjacent the armature and juxtaposed to the north poles of the pole piece 23a. It will be apparent that a current in the winding 25 will oppositely magnetize the opposite ends of the armature element 24, producing a force tending to rotate the armature about its midpoint in direction depending upon the direction of the current in the winding 25 and with a force proportional to the amplitude of the current.

As shown in Fig. 3, the pole pieces 23a and 231) are rigidly mounted with respect to the permanent magnets 53 and 54 and the frame 26 of the mechanism by four screws 27 extending through apertures in extensions 23 of the bight portions of the pole pieces 23a and 2312, the two pole pieces being maintained in accurately spaced relation to each other by the permanent magnets 53 and 54 interposed between the extensions 28 of the respective pole pieces.

Rotative movement of the armature element 24, as previously described, varies the pressure delivered to the passages 20 and 21 in the following manner: The opposite ends of the armature 24 are juxtaposed to and in closely spaced relation to nozzles 39 and 31, respectively. The nozzle 31 has a passage 32 connecting to a chamber 33 which in turn is connected by a restricted orifice 34 to the pressure port and to the passage 21 leading to the left end of the valve cylinder 15. The passage of the nozzle 31 is similarly connected by a restricted passage to the pressure port 15a, and to the passage 20 leading to the right end of the valve cylinder 15.

When the armature element 24 is in neutral position, it equally impedes how of fluid from the nozzles 30 and 31, respectively, and the pressures in the motor passages 2i and 21 are equal so that the piston 16 remains in neutral position. If the armature 24 is rotated counterclockwise in response to cnergi'zation of the coil 25 to move closer to the nozzle 30 and farther away from the nozzle 31, then the fiow through the nozzle 36 will be impeded to a greater extent than the flow through the nozzle 31. This causes the pressure to rise in the chamber 33 and in the left end of the valve cylinder 15, whereas the freer release of fluid from the nozzle 31 reduces the pressure in the right end of the valve cylinder, thereby producing movement of the valve piston 16 to the right. If the armature element 24 is rotated clockwise, the pressures are reversed, to move piston 16 to the left.

As previously indicated, valves of this type can be made extremely sensitive and capable of very rapid response, but when so constructed, they are apt to be unstable and oscillate or sing. In accordance with the present inventions, such undesired oscillations are reduced or r r 3. prevented by providing a'damping action on the armature element 24.

Armature element 24 is supported for limited, restrained movement by a pair of leaf spring elements 37 and 38, respctively, rigidly connected to the armature element adjacent opposite ends thereof and extending from the armature at an angle of approximately 45 for an appreciable distance beyond which the ends are turned down and secured to supporting clamps 39 and 40, respectively, which are adjustably mounted on housings 41 and 42 which surround the nozzles 30 and 31, respectively. Each of the clamps 39 and 40, as shown in Fig. 2, is split and is adapted to be tightened about its supporting housing by a screw 43. By looseniugthe screw 43 of either clamp, the clamp can be adjusted axially with respect to'the axis of the associated nozzle to center the related'end of the armature element 24 in a desired position with respect to the magnet structure and the nozzle structure.

In normal operation, the entire mechanism 22 is enclosed ina hermetically sealed housing or cap 47 and is filled with oil. 'By virtue of the fact that the intermediate portions of the leaf springs 37 and 38 are relatively wide and have a substantial area, their movement is inherentlydamped to a certain extent by the ambient liquid in which they are immersed.

However, I find it desirable to further increase this damping efiect by providing adjacent the intermediate flat portion of each leaf spring a stationary damping vane v48 or 49, respectively. Each damping vane 48.0r 49,

in addition to its rather large flat surface juxtaposed to the associated leaf spring 37 or 38, has a supporting or base portion bent at an angle and clampedto the upper pole piece'23a by a clamp strip 50 and screws 51. By loosening the screws 51, each damping vane 48 can be accurately adjusted to a desired closely spaced relation to j the associated leaf spring 37 or 38.

' scribed, obvious modificationstwill occur to a person skilled in the art, and'I 'do not desire to be limited to the details shown and described.

I claim:

1.. An electrohydraulic' valve comprising: an electric .motor having an element movable within a fixed short path and means responsive to an electric current for urging said movable element into a position within said path dependent upon the strength and polarity of said current; valve means controlled ,by said movable element andincluding a stationary nozzle and a flow-impeding element on said movable element movable with respect to said nozzle in response to said movement of the mov- -able element in said path; a damping vane secured to said movable element for movement therewith to damp movement of said movable element by the frictional resistance to movement of said vane presented by the ambient fluid; and a stationary vane juxtaposed to said damping vane in close proximity thereto.

2. Apparatus according to claim 1 in which said vanes are substantially flat. t

3. Apparatus according to claim 2 in which said vanes are so positioned relative to said path of movement of said movable element that movement varies the spacing between said vanes.

4. An electrohydraulic valve comprising: an electric motor having an element movable within a fixed short path and means responsive to an electric current for urging said movable element into a position within said path depending upon the strength and polarity of said current; valve means controlled by said movable element and including a stationary nozzle and a flow-impeding element on said movable element movable with respect to said nozzle in response to said movement of the movable element in said path; adampingovane secured to said.

movable element for movement therewith to damp move ment of said movable element by the frictional resistance to movement of said vane presented by the ambient fluid; and stationary supporting means in spaced relation to said movable element; said damping vane comprising a leaf spring attached at one end to said movable elemeut and at the other end to said supporting means.

5. Apparatus according to claim 4 in which said leaf spring has an intermediate flat portion, and a stationary vane juxtaposed to said flat portion in close proximity thereto;

'6. Apparatus according to claim 4 in which said stationary supporting means comprises a cylindrical supporting member in fixed concentric relation to said nozzle; and a clamp on said cylindrical supporting member rotatably and axially adjustable thereon, said other end of,

said leaf spring being attached to said clamp for adjusting movement therewith.

7. Apparatus according to claim 1 in which said movable element and current responsive means are symmetrical about an axis of movement and said flow-impeding element and nozzle are on one side of said axis; a second stationary nozzle and second flow-impeding element on said movable element'symmetrically disposed on the, opposite side of said axis with respect to the first nozzle and flow-impeding element, so that movement of the movable element about said axis moves one flow-impeding element toward and the other away from its associated nozzle; said one damping vane being connected to said movable element on, one side of said axis; another damping vane on said movable element symmetrically disposed on the opposite side of said axis with respect to said one 'vane; and another stationary means juxtaposed to said other clamping vane in close proximity thereto Great Britain min, 194 

